1. Field of the Invention
The present invention relates to means of recording information, and more particularly to radiation-sensitive materials and methods of recording information on these materials.
Hereinafter by a radiation-sensitive material is meant a material sensitive to electromagnetic and corpuscular radiation.
The proposed material and method can be employed for recording binary information in memory units of electronic computers, in video-recording equipment, laser recording devices and other information recording means.
2. Description of the Prior Art
Methods of recording information by means of electromagnetic and corpuscular radiation are widely known. Among the materials for carrying out these methods there is known a sensitive element (cf. U.S. Pat. No. 3,637,381) comprising a metallic layer and an inorganic material layer deposited thereon and capable of forming interaction products therewith when exposed to electromagnetic actinic radiation, said interaction products having physical and chemical properties different from those of the metallic layer and of the inorganic material layer. In this case, as a result of such interaction there occurs etching of the metallic layer.
Recording information upon the above element is done by exposing the element to actinic radiation within the time sufficient for the complete reaction process, the amount of the interaction product being proportional to the duration of exposure and the intensity of radiation.
Due to a continuous partial interaction between the inorganic material and the metallic layer the above element has a low chemical stability even without being exposed to radiation, if the inorganic layer is a layer of a semiconductor with a width of the forbidden band of over 2 eV, i.e. a semiconductor which provides a high sensitivity of the element and a wide range of its spectral sensitivity. In addition, this element integrates the impinging irradiation corresponding to the range of a proper absorption of the inorganic layer. Because of a low reliability of the recorded information storage and a low fidelity of the information readout resulting from these disadvantages, the above sensitive element is not suitable as an information carrier in the devices wherein information is recorded and read out either by electromagnetic or corpuscular radiation.
The number of readouts from the information carrier made from the above sensitive element is also limited, and therefore the power density of the radiation for reading information should be much lower than that of the recording radiation, which, in turn, reduces a signal-to-noise ratio while reproducing the information.
There is known a method of recording information upon a radiation-sensitive element by electromagnetic irradiation (cf. Japanese Patent No. 49-81036, N. Cl. 103 KO) which is characterized in that the radiation-sensitive element, after being exposed to electromagnetic radiation, is subjected to a thermal treatment.
There is also known a material for carrying out this method, comprising a metallic layer made from silver, or copper, or nickel, or thallium, an inorganic material layer made from antimony chalcogenide, or bismuth chalcogenide, or arsenic chalcogenide, and a separation layer disposed between the two first layers and made from a material which is inert with respect to said layers. Generally, the metallic layer is deposited on a radiation transparent support backing. Over the metallic layer there are deposited in succession a separation layer and an inorganic material layer capable of interacting with the metallic layer to form the interaction products when exposed to actinic radiation, said interaction products having physical and chemical properties different from those of the metallic layer and the inorganic material layer.
The usual materials used for the metallic layer are silver, copper, nickel, tellurium, gallium, aluminum, bismuth, gold, cadmium, chromium.
The materials which are used for the inorganic layer are halogenides, dioxides, arsenides, selenides, tellurides, binary and ternary systems of chalcogenide arsenic glass, antimony, bismuth.
The separation layer of this radiation-sensitive material is formed from inorganic materials, for instance, arsenic trisulfide.
The above radiation-sensitive material features a high stability of chemical properties during a long-term storage for the metallic layer is in contact with a semiconductor having a small width of the forbidden band. However, this high stability of chemical properties is manifested only if said sensitive material is not exposed to actinic radiation. Otherwise, i.e. under the action of actinic radiation of even a low intensity the structure of said radiation-sensitive material changes masking the useful information. This, in turn, results in a lower reliability of the information storage and makes it necessary, while reading out information, to decrease the radiation power density by several orders as compared with the radiation power density required for recording information, which affects the fidelity of the read-out thereof.
It is quite natural that these disadvantages of the above sensitive element present certain difficulties when it is utilized as an information carrier. Moreover, the necessity of thermal treatment thereof leads to an increased consumption of energy.